It is a goal in the art of artificial porcelain dental restorations and veneers to match as closely as possible the appearance of the patient's surrounding natural dentition. In particular it is desirable for the color of the artificial restoration or veneer to match as closely as possible the color of the adjacent teeth. As natural tooth color varies among individuals, it is necessary for the dental technician or dentist to be able to control the color to properly match the natural teeth of each individual patient.
There are many types of porcelain dental restorations. The technique used for color matching will vary depending on the type of porcelain restoration made. Modern porcelain restorations typically include porcelain bonded to an underlying metal substructure. The porcelain typically includes an opaque base layer, an intermediate layer of dentin porcelain, and an outer layer of enamel porcelain. In some cases, the metal substructure is covered with a bonding agent to promote bonding of the porcelain to the metal. The color of the completed restoration is a function of the color and opacity of the opaque, dentin, and enamel layers of the porcelain, the color of the metal substructure, and the color of the bonding agent in cases where it is used. In these restorations, the dental technician adjusts the color of the total restoration by adjusting the colors of each of the components of the restoration. Most often, the underlying metal substructure gives an unappealing grayish cast to the restoration. Attempts to hide the gray color result in a thicker and more opaque porcelain which tends to look unnatural when compared to the natural translucency of human teeth. This is particularly true in cases where very thin restorations are used.
A new type of metal porcelain restoration has been introduced as described in U.S. Pat. No. 4,392,829, issued July 12, 1983, the complete disclosure of which is incorporated herein by reference. That invention relates to a dental restoration wherein the metal substructure is a thin platinum foil having a textured surface to which porcelain is directly applied. The foil is swaged over a die of the tooth, the foil is sand blasted to texturize the surface, porcelain paste is applied directly to the textured surface of the foil, and the restoration is baked to harden the porcelain and bond it to the foil. The invention eliminates the need for the application of a bonding agent to the foil, which had previously been necessary to promote adhesion of the porcelain to the foil. The platinum foil, however, has a gray appearance which presents the same color matching problems experienced in restoration of the prior art.
Dental bridges are a kind of porcelain dental restoration designed to fill edentulous regions. Existing dental bridges suffer the same shortcomings as other dental restorations. In addition, because of the greater size, dental bridges have additional breakage problems. In particular, at the joints between the teeth on either side of the edentulous region and the edentulous region itself, the metal is thin and often breaks.
Rather than using an entire dental restoration, dental veneers are sometimes used when it is desirable to replace worn-down portions of teeth or to attempt to provide a more desirable color to a discolored tooth.
There are various types of conventional dental veneers, all are typically made entirely of porcelain without the inclusion of a metal substructure. The conventional veneers generally have three porcelain layers: an opaque base layer, an intermediate layer of dentin porcelain, and an outer layer of enamel porcelain. Typically, these veneers have a total thickness of greater than 500 microns.
These dental veneers are bonded to the patient's natural tooth by first etching the surface of the tooth to promote bonding. This etching technique is well known in the art. After etching, the porcelain dental veneer is bonded to the tooth surface using a bonding agent. The use of these all-porcelain veneers does not mask severe discoloration of the underlying tooth and is also affected by the color of the bonding material. Moreover, the veneer does not have great strength by itself. Thin veneers, which are more desirable from an aesthetic viewpoint, are easily broken when being bonded. Furthermore, in a posterior occlusal usage, the tooth must be ground extensively to allow the use of a thicker occlusal onlay or a crown. While a platinum or palladium foil could be used as the metallic base of a metal porcelain dental veneer, as with dental restorations, the gray color of the foil would prevent a natural looking veneer especially because veneers are thin.
It is known in the art that gold metal has a more esthetically pleasing color when used as a substructure in dental restorations. Gold colored alloys, however, do not have sufficient tensile strength and hardness to serve as dental restoration substructures. One attempt to provide a metallic substructure having both suitable physical properties and an esthetically pleasing color involved a bimetallic backing having a thicker layer of white colored alloy and a thinner layer of gold colored alloy, as described in U.S. Pat. No. 2,572,377 issued Oct. 23, 1951 to R. E. O'Morrow. This backing disadvantageously requires the preparation and welding together of two distinct alloy materials.
It would be desirable to have for use in metal porcelain restorations, veneers and dental bridges, a foil having a color more similar to that of natural dentin in order to facilitate matching the complete restoration with the surrounding natural teeth. It would further be desirable to have a foil formed of a single alloy that is relatively easy to prepare. Furthermore, it would be desirable that the foil be heat resistant to minimize distortion when the overlaying porcelain is fired, yet sufficiently malleable to ensure proper fit of the foil to the die, and ultimately of the finished restoration to the mouth.
Such a metal foil could be fashioned into the metal substrate of a metal porcelain dental restoration or dental bridges, or the metal base of a metal porcelain dental veneer by use of conventional techniques or by the use of application of isostatic pressure as described in U.S. Pat. No. 4,794,774, issued Jan. 3, 1989, the complete disclosure of which is incorporated herein by reference.